1. Field of the Invention
This invention relates to apparatus and methods for forming fibrous pads, and more specifically to apparatus and methods for forming discrete pads of a desired shape and profile.
Reference to "shape" throughout this application, including the claims, in describing the structure of a fibrous pad, refers to the configuration of the pad in plan view.
Reference to "profile", as used throughout this application, including the claims, in describing the structure of a fibrous pad, refers to a varying weight distribution of fibers in the pad such that the pad has a predetermined region with a weight of fibers per unit area therein which is different than the weight of fibers per unit area in at least one other predetermined region of the pad.
2. Description of the Prior Art
Many sanitary products, such as disposable diapers, sanitary napkins and the like, utilize an absorbent fibrous pad as one component thereof. This pad, in many instances, must have a specific shape which can be reproduced in an economical mass production operation. One prior art apparatus for producing discrete fibrous pads is disclosed in U.S. Pat. No. 2,940,133, issued to Heritage. This patent discloses an apparatus employing a drumtype condenser upon which fibrous pads are formed. The condenser is masked to define air-permeable surfaces defining the shape of fibrous pads to be formed. The air-permeable surfaces are separated by air-impermeable surfaces which are disposed substantially in the same plane as the air-permeable surfaces. It is difficult to form fibrous pads having the specific shape of the air-permeable surfaces in a repeatable fashion by utilizing an apparatus such as is disclosed in the Heritage patent. One major reason for this difficulty is that air-suspended fibers which are initially directed toward the masked, air-impermeable surfaces of the condenser are deflected to the perimeter of the unmasked, air-permeable surfaces by a vacuum applied from within said condenser. The air suspension of fibers impinges on the boundaries of the air-permeable surfaces at various angles to cause random deposits of fibers adjacent the perimeters of the unmasked surfaces of the condenser. These random deposits cause distortions in the shape of the formed fibrous pads.
Other prior-art apparatus for forming fibrous pads have employed drum-type condensers with three-dimensional pad-receiving compartments extending inwardly from a peripheral surface thereof. Such prior-art apparatus are exemplified in U.S. Pat. No. 3,518,726, issued to Banks; and in U.S. Pat. No. 1,950,765, issued to Winter. These drum-type condensers, as well as the drum-type condenser disclosed in the Heritage patent, have several deficiencies. In order to obtain controlled pad formation, an air suspension of fibers should be directed either tangent or perpendicular to the forming run of a pad-formation assembly. When the air suspension of fibers is directed tangent to the forming run a cloud of air-suspended fibers is established above the forming run. This cloud can be directed in a controlled manner into the pad-receiving compartments by a partial vacuum created through a vacuum source disposed below said forming run. When the air suspension of fibers is directed perpendicular to the forming run the fibers also are easily diverted into the pad-receiving compartments in a controlled manner to establish controlled pad formation. When the air suspension of fibers is directed toward the pad-formation assembly at orientations other than tangent or perpendicular to the forming run, uncontrolled, non-uniform fiber distribution occurs at either the trailing or leading edge of each compartment, depending upon the specific orientation of the stream of air suspended fibers relative to the compartments. Theoretically, no complete pad-receiving compartment or discrete pad-receiving area of a drum-type condenser is oriented either perpendicular or tangent to a stream of air suspended fibers at any given time during the pad forming operation. Practically, only about 90.degree. of the periphery of a drum-type condenser at any given time during the pad forming operation is so oriented with respect to a stream of air suspended fibers that adequate control of pad formation can be achieved.
Apparatus employing drum-type condensers are speed limited by the fact that a major portion of the condenser surface, at any given time, is not properly oriented to be utilized in forming shaped pads in a controllable manner. To increase the pad output in apparatus employing a drum-type condenser, the condenser must be operated at extremely high speeds, and/or the drum-type condenser must have an extremely large diameter such that 90.degree. of the periphery of the condenser represents a large surface upon which several discrete pads can be formed. Operating a drum-type condenser at extremely high speeds will cause the fibers to be thrown off the condenser by centrifugal force, and thereby cause uncontrollable variations in the formed pads. Large drum-type condensers are cumbersome to handle, and difficult to assemble on a mounting axle. When such a condenser has to be changed; for example, when a fibrous pad having a different shape is to be formed; heavy equipment, such as a crane, normally must be employed. If the drum-type condenser is made in segments, changing the condenser will not require the use of heavy equipment; however, assemblying a segmented condenser is time consuming, and involves the additional problem of establishing effective seals between the segments.
In the Banks patent (3,518,726) each pad-receiving compartment has a varying thickness in a circumferential direction resulting from the formation of each compartment by arcuate side plates and a substantially flat perforated bottom plate. In this construction the pad-receiving compartments are thicker in the center than at opposed ends, and the pads formed in such compartments will assume the profile of the compartments. The banks+ drum-type condenser lacks versatility since a pad having only one specific profile can be formed therein, i.e. a pad having a greater weight of fibers per unit area in the center region than in adjacent end regions. To form fibrous pads with a different profile, the drum-type condenser must be replaced by one having surfaces therein defining a compartment having a profile corresponding to that of the pad to be formed. This change of condensers can be a cumbersome, difficult to achieve task, as explained earlier in this application. Furthermore, the specific configuration of surfaces defining compartments of different profiles may be fairly intricate and difficult to form in drum-type condensers.
In many applications it is desirable to form a fibrous pad which is profiled in the cross-machine-direction, i.e. a fibrous pad wherein different predetermined regions having different weights of fibers per unit area therein are spaced from each other in the cross-machine-direction. The apparatus disclosed in Banks is designed only for forming fibrous pads which are profiled in the machine-direction. Banks does not suggest an apparatus for forming fibrous pads profiled in the cross-machine-direction.
In the Banks apparatus, the pads can be somewhat easily removed from the drum-type condenser because of the tab connection between adjacent pads. To further explain, if one of the pads is removed from a compartment it will tend to lift adjacent pads out of their respective compartments as a result of the force transmitted to these adjacent pads through the tab connections. However, when fibrous pads are formed as discrete, separate members, a problem exists in removing such pads from three-dimensional compartments in drum-type condensers. In order to remove discrete pads from the compartments, the vacuum applied through the lower surface of the compartments must be cut off. When the vacuum is cut off air is permitted to become entrapped between fibers in the pads to expand the pads into engagement with the peripheral side walls defining the compartments. This expansion of fibers creates frictional drag against the side walls, and prevents easy removal of the pads from the compartments.
Apparatus employing a pad-formation assembly having a substantially linear forming run, and allegedly operable to form pads of a particular shape in a repeatable fashion is disclosed in U.S. Pat. No. 2,949,646. The apparatus disclosed in this patent utilizes a three-dimensional masking frame assembly having individual masking elements with openings therein which define the shape of the pads to be formed. A conveyor system movable in synchronism with the masking frame assembly is disposed beneath the three-dimensional masking frame assembly, and this conveyor system is foraminous along its entire extent, i.e. the conveyor system is not provided with masked, air-impermeable regions and unmasked, air-permeable regions. Each masking element has a pad-defining opening, and the regions outside of this opening are foraminous. The fibers carried in an air stream are directed toward the conveyor and masking elements from above the masking elements. The fibers directed into the openings of the masking element deposit on the conveyor to form pads generally having the shape of the opening. The remaining fibers are deposited on the foraminous regions of the masking elements, and therefore are not utilized to form pads. The fibers deposited on the foraminous regions of the masking elements should be recycled back into the process to achieve optimum utilization of fibers. Equipment for recycling the fibers increases the complexity and cost of the apparatus.
The apparatus disclosed in U.S. Pat. No. 2,949,646, does not utilize a vacuum source to hold the formed pads on the conveyor at the point of separation between the conveyor and the three-dimensional masking frame assembly. Therefore, some distortion or destruction of the pads may occur because of a stronger affinity of the fibers for the masking frame assembly, than for the underlying conveyor.
Air directed through regions of the conveyor underlying the foraminous portions of the masking elements may cause fibers to displace from the region defined by openings in the masking elements to become trapped between the conveyor and the foraminous portions of the masking elements. The displacement of fibers occurs because the regions of the conveyor underlying the foraminous portions of the masking elements are not masked to the passage of air. These trapped fibers can adhere to the pads which are formed and thereby cause distortions in the finished pad. This prevents the repeatable reproduction of fibrous pads of a required shape.
U.S. Pat. No. 3,501,813, issued to Lee et al, discloses an apparatus for making a continuous, profiled fibrous web having a longitudinally extending medial regions with a greater weight of fibers per unit area therein than longitudinally extending flanking side regions. The Lee et al apparatus requires the use of baffles to engage an air-suspension of fibers within a conveying duct to deflect the fibers into overlying relationship with a medial region of a foraminous conveyor upon which the web is to be formed. This deflection increases the volumetric flow rate of the deflected portion of the air suspension of fibers. Lee et al allegedly compensates for this increased flow rate by regulating valve openings in a vacuum box disposed behind the foraminous conveyor to permit the region of the vacuum box underlying the medial region of the foraminous conveyor to accommodate the increased air flow.
The Lee et al apparatus has several deficiencies. First, the use of baffles to deflect the air suspension of fibers results in a more complex apparatus than one in which deflecting baffles are not used. Second, when it is desired to form continuous fibrous webs with different profiles, the baffles must be rearranged within the duct through which the air suspension of fibers is directed. This rearrangement of baffles can be a difficult and a time consuming task. In some instances the baffles may not be relocatable to a required position to permit formation of a continuous fibrous web having a required profile. Therefore, the Lee et al apparatus lacks the desired degree of versatility to easily permit its use for forming continuous fibrous webs having many different profiles.
U.S. Pat. No. 3,598,680, issued to Lee, discloses an apparatus for forming continuous fibrous webs having a longitudinally extending medial region with a greater weright of fibers per unit area therein than in flanking side regions. This apparatus is described as an improvement over the Lee et al apparatus discussed above, and employs separate fiberizing devices, and separate formation chambers to form the continuous, profiled fibrous web. This apparatus lacks versatility in permitting the formation of continuous fibrous webs having many different types of profiles. In order to vary the profile of a continuous fibrous web, extensive modifications to the equipment are required. For example, the formation chambers at various locations would have to be reoriented to overlie different sections of the foraminous conveyor upon which the web is to be formed. This requires considerable machine reconstruction, and therefore is highly undesirable.
The apparatus and method disclosed in both the Lee et al and the Lee patents relate to the formation of continuous profiled webs, and in no way suggest a method and/or apparatus for forming discrete fibrous pads having a desired shape and profile, which can be varied in a simple and reliable manner.
The method of continuous web formation disclosed in both the Lee et al and Lee patents requires the formation of separate fibrous strips which overlap each other in certain regions to define a thickened region, i.e. a region having a greater weight of fibers per unit area therein than in non-overlapped regions of the strips. Stating this another way, the method disclosed in both the Lee et al and the Lee patent requires the formation of at least a portion of a thickened region simultaneously with the formation of a different region having a lesser weight of fibers per unit area therein than in the thickened region. Therefore, certain stages of the web forming operation disclosed in both the Lee et al patent and the Lee patent depend upon the masking effect, i.e. resistance effect, of a portion of the web formed in a specific predetermined region during a previous stage of the web forming operation. In a later stage of the web forming operation the fibers will be deposited initially in an unformed region of the web since the resistance to air flow in such unformed region is considerably less than the resistance through a partially formed region of the web. As the web forming operation proceeds, the resistance to air flow increases in what was the unformed region of the web as a result of the build up of fibers in said region, and the air suspension of fibers tends to divide to deposit fibers in different predetermined regions. This division of the air suspension of fibers is not controllable, since the changing resistance characteristics resulting from the build up of fibers in different predetermined regions cannot be determined or controlled easily during the web forming operation. Furthermore, as the weight of fibers per unit area in one predetermined region approaches the weight of fibers in a different predetermined region a self-leveling effect occurs which tends to destroy the profile of the web and thereby create an unprofiled web having a substantially uniform weight of fibers per unit area throughout. Therefore, the methods of web formation disclosed in both the Lee and the Lee et al patents preclude the controlled formation of profiled pads in which the weight of fibers in different predetermined regions are different but quite close to each other, and makes difficult to varying degrees all profiles except those in which the differences in the weight of fibers per unit area in different predetermined regions are extreme.